100 
HAROLD'S DISCUSSIONS. 
Thus from sea and lake, river and pond, field and 
forest, water is constantly rising into the air as invisi¬ 
ble vapor. ^N’ot only in the warm summer days, but 
even in the cold weather of winter, is this true. A 
few years ago I placed blocks of ice out-of-doors dur¬ 
ing a spell of weather so cold that not even the noon¬ 
day sun could produce any thawing, but the ice-blocks 
grew gradually smaller. I believe the water evapo¬ 
rated from them without visible thawing. We do not 
often stop to think how much water is lifted skyward 
day by day the year through. Men who have studied 
the subject a great deal have estimated that not less 
than fifty million tons of water are evaporated on the 
surface of the earth every second. 
The warm currents of air carry all this water from 
one to eight miles into the atmos23here. There it 
collects into clouds of various shapes and sizes in ac¬ 
cordance with the temperature and currents of the 
higher air. 
SHAPE OF CLOUDS. 
At first we are inclined to think that there are so 
many different kinds of clouds that it is almost useless 
to attempt to classify them. While I must admit 
that one kind often shades into another, careful ob¬ 
servation has enabled me to discover three fundamental 
forms which differ generally according to the altitude 
at which they ride the winds. 
Scientists have given them names which are de¬ 
scriptive of their appearance. 1. The cirrus (curl) 
dwells in the upper air from eight to ten miles above 
